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=. DiA 1. --- .../.• '. \ + - :2.-L_.:-11 --9--:.2 ar•i.•'ti*.1 The interior lighting system is built on a piece of perforated board which is mounted inside the roof with double-sided foam tape. Above: The author has installed marker light drcuits in observation cars made by Rivarossi, Bachmann Spectrum, Atheam, Rivarossi, and Con-Cor and in cabooses made by Model Die Casting (plastic) and Overland Models (brass). Left: Patrons in this Lone Pine & Tonopah cafe-lounge car enjoy nice steady light as the car is being switched into an express train. delay when voltage is lost, while increasing the lamp current draw reduces the delay time. This circuit requires about 6.5V on the rails for the regulator to provide any output voltage, so the lamps will not turn on until that voltage is applied. As the track voltage increases. the regulator maintains constant voltage and lamp brightness so the lamps will not burn out. A benefit of this action is the current draw of the car does not increase at higher track voltages. With the bridge rectifier, this circuit works for either direction of travel. The bridge rectifier can be replaced with a single diode which will allow the lamp to turn on at about 0.7V less, but lights will then only work in one direction of travel. Microbulb marker lights This circuit can also be used for car marker lights using 1.5 to 1.8V microbulbs. The microbulbs should be wired in series with each other and with a resistor to limit the voltage across each bulb to about 1.5V. Otherwise the five-volt regulator output would burn them out. Another approach is to substitute an adjustable voltage regulator such as the 317T for the 7805 regulator and adjust its output for 3V. This will also allow the bulbs to light at a lower track voltage. LED marker lights Figure 2 shows a circuit using small, red LEDs for caboose or observationcar marker lamps that operate only when the track polarity is set for forward travel. In this circuit, the forwardvoltage-drop in two LEDs wired in series limits the capacitor voltage to about 4V and does not need the voltage regulator of fig. l's circuit. While the capacitor voltage is limited by the LEDs, the LED current is to about 20mA with a track voltage of 15V. My LEDs begin to glow with a lew volts at the track and get brighter as the voltage increases. LEDs work well here because they draw less current All·-4 /69 . . - :.-1 f,.•-/m/.f ./0 . L : determined by the series resistor and .9/2 the track voltage. I selected a resistor value of 560fl to limit the LED current JilEiIt. 1•t... rvgz' •', than lamps and provide acceptable brightness over a relatively wide range of current. For observation cars with a single There's plenty of room for marker light red light over the rear platform. you circuits in cabooses, but be careful to avoid can substitute one red LED for the two possible shorts in brass model installations. shown in this circuit. Now the capacitor will only charge to around two volts, but it'11 still provide protection against flickering and will turn on at a lower Parts sources track voltage. NOTE: Do not use more than two LEDs in series as this will allow more than 5V to reach the capacitor. Constant brightness diodes There is another trick we can use to help maintain stable brightness over a wider range of locomotive speeds. Many modelers use diode systems to provide "constant" brightness of the locomotive lights. These diode systems all •rob" the locomotive of the first 1.6 to 2.35V applied to the track. This is beneficial since the car lighting circuits will receive that much more All Electronics P. 0. Box 567 Van Nuys, CA 91408-0587 Digi-Key Corp. 701 Brooks Ave. South P. 0. Box 677 voltage before the locomotive moves used for this artide were obtained from and therefore reach full brightness at Thief River Falls, MN 56701-0677 The .22mf 5.5V DC capacitors•which I All Electronics and are listed as catalog lower locomotive speeds. We can number CBC-4. I recommend that you extend this effect even further by test a sample capacitor before ordering adding more di6des in series with our in large quantities. passenger locomotives.. MOREL RAILROADER 99 1 ililliuillk r -1-R , csT,<r . / Voltage regulators, resistors, and diodes are available at Radio Shack and other sources. Memory capacitors are available from the following sources: